Zinc-steel sacrificial anode ground rod

ABSTRACT

A GROUND ROD IS MADE FROM A SACRIFICIAL ANODE CORE INSIDE A HARDENED SHEATH OR JACKET. THE SHEATH IS SPLIT LONGITUDINALLY, AND THEN THE LONGITUDINAL CORNERS OR EDGES ARE TURNED IN TO PROVIDE A LOCKING KEY WHICH FITS INTO LONGITUDINAL GROOVES ON THE ANODE CORE, THUS COMPLETING THE GROUND ROD. THIS MAKES A STRONG ROD WHILE EXPOSING THE ANODE CORE. THIS WAY, A STEEL JACKET, FOR EXAMPLE, PROVIDES THE MECHANICAL STRENGTH REQUIRED FOR A DRIVEN GROUND ROD AND A EXPOSED ANODE (FOR EXAMPLE, ZINC) PROVIDES A SACRIFICIAL ANODE. OTHER ANODE MATERIAL SUCH AS MAGNESIUM AND ALUMINUM MAY ALSO BE USED.

June 18, 1974 J TQEDTMAN ETAL 3,817,852

ZINC-STEEL SACRIFICIAL ANODE GROUND ROD Original Filed Sept. 23, 1969 iJ.A. Toedtman 5 I By G.W. Petri and G. Kayariun A TTO/P/VEY UnitedStates Patent Int. Cl. C23f 13/00 US. Cl. 204-197 4 Claims ABSTRACT OFTHE DISCLOSURE A ground rod is made from a sacrificial anode core insidea hardened sheath or jacket. The sheath is split longitudinally, andthen the longitudinal corners or edges are turned in to provide alocking key which fits into longitudinal grooves on the anode core, thuscompleting the ground rod. This makes a strong rod while exposing theanode core. This way, a steel jacket, for example, provides themechanical strength required for a driven ground rod and an exposedanode (for example, zinc) provides a sacrificial anode. Other anodematerial such as magnesium and aluminum may also be used.

This is a continuation of application Ser. No. 860,214, filed Sept. 23,1969, now abandoned.

This invention relates to electrical power distribution systems and moreparticularly, means for protecting underground equipment againstelectrolytic corrosion.

The basic theory behind corrosion of metals is that some of the metallicmolecules, immersed in an electrolyte, disassociate themselves into ionswhen they free electrons. This theory of metal corrosion is ratherstraightforward. However, it is difficult to evaluate the relativeimportance of the many different factors which aifect undergorundcorrosion. In fact, the conditions under which corrosion occur are sopoorly defined that the theory is often more helpful in explaining why acorrosion has already taken place rather than predicting what is to beexpected.

Usualy, the metallic state (which is a high energy form) is uncommon innature where most metals are found as oxides or compounds of oxides(which are a low energy form). These oxides achieve the higher state ofinternal energy during a refining process which ultimately leads to auseful metal. Corrosion is the process by which the metal returns fromthis unnaturally higher level of energy to the original lower energylevel of the oxide state.

For instance, when iron and copper are immersed in a common electrolyte,iron molecules have a greater tendency than copper molecules to losetheir electrons, become positive ions, and disassociate themselves fromthe metal. When this occurs, the iron becomes negatively charged withrespect to the electrolyte or liquid in which it is immersed. Therefore,a galvanic couple is formed between the iron and copper. The resultingimbalance of electrons causes a current to flow from the iron to thecopper. As the electrons are deposed at the copper, a chemical reactionoccurs in the iron to form an oxide. From this, it is clear that if ironand copper are immersed in a common electrolyte, the oxidization of theiron is greatly accelerated.

A typical underground electrical power distribution system, and thecomponent parts thereof, have all of the ingredients for making acorrosion cell. Although the mild steel transformed tank is oftenprotected with a surface coating, scratches, nicks, and chips expose thebare steel. The soil with its accompanying moisture or ground water isthe electrolyte. Thus, a corrosion cell exists between the bare steeland any exposed copper.

To overcome this problem, another metal (sometimes called a sacrificialanode) is often immersed in the electrolyte to form another galvaniccouple. This other metal is selected from a class of metals havinganodic voltage potentials relative to steel. Then, the other metal givesup its electrons, is broken down, and sacrified to absorb corrosivepotentials, thus diverting these potentials from the galvanic coupleformed by copper and steel. Fundamentally, therefore, cathodicprotection consists of impressing, on an underground structure, anelectromotive force which makes the entire structure cathodic withrespect to the adjacent soil.

Accordingly, an object of the invention is to provide new and improvedanodic or cathodic protection of underground electrical equipment. Inthis connection, an object is to mechanically protect the sacrificialmetal without affecting its function of making the equipment cathodicwith respect to the ground.

In keeping with an aspect of the invention, these and other objects areaccomplished by providing a zinc-steel ground rod for the dual purposeof completing a sacrificial anode in a galvanic couple between the zincand other metals and of grounding the electrical equipment to preclude aheavy build-up of electrical potentials thereon. To protect the zincagainst mechanical damage when it is driven into the ground and toinsure continued good electrical connections, the zinc is surrounded bya split steel jacket. The steel is crimp connected into the zinc to makea rugged unitary structure. The zinc exposed by the split provides theanode.

The above mentioned and other features and objects of this invention andthe manner of obtaining them will become more apparent, and theinvention itself will be best understood by reference to the followingdescription of an embodiment of the invention taken in conjunction withthe accompanying drawings, in which:

FIG. 1 is a cross-section view which shows the end of a solidsacrificial anode rod as it appears at the start of a manufacturingprocess;

FIG. 2 shows a cross-section of the end of the same rod after it hasbeen initially formed, as by being extruded or drawn through a firstdie;

FIG. 3 shows the end of a cross-section of the same rod after it isdrawn through a second die;

FIG. 4 is a cross-section end view which shows a galvanized steel sheathor jacket after an initial forming step;

FIG. 5 shows the combination of the steel sheath or jacket of FIG. 4 andthe sacrificial anode rod of FIG. 3;

FIG. 6 is a perspective view which shows successive die reductions ofthe combination rod of FIG. 5; and

FIG. 7 is a perspective view which shows a completed drivable, bi-metalsacrificial anode, ground rod.

A below grade housing or vault for electrical equipment, for example,may be either coated mild steel or stainless steel. In keeping with theusual electrical installation practice, all of the parts of the housingand equipment therein are connected together by means of common groundwiring which is, in turn, connected to a ground rod. In the case of amild steel housing in an electrolyte of ground water, the furtheraddition of a zinc, alumi num, or magnesium sacrificial anode greatlyreduces the corrosion rate of the steel.

In greater detail, the potential standing on mild steel, per se, isapproximately 0.4 volts. The steel is protected if its potential can bedriven to 0.85 volts. This is accomplished by electrically connecting,say a zinc anode to the steel because the zinc is more active than themild steel, and it supplies an electron flow to the steel which drivesit further negative. Assume, for example, that a transformer tank has asurface resistance of 3,000 ohms, assume also 15 ohms for theelectrolyte ground waterand scarificial anode,.and .01 ohms for aconcentric copper neutral. A zinc anode has a driving voltage of 0.25volts, and a magnesium anode has 0.9

volts. The current can now be calculated. Using these magnesium. Thus,in a typical situation, a pound of zinc would last 2.4 years and a poundof magnesium would last 1.1 years.

7 To make the inventive ground rod, a bar of sacrificial anode material,such as zinc, aluminum, or magnesium, is drawn through a Vaughn drawblock to have a generally circular cross-section 20 with a specificdiameter. For example, as received, the bar stock might be a coil whichis nominally circular in cross-section and approximately three-quartersof an inch in diameter, but its circumference may be irregular with anydiameter varying by, perhaps, a sixteenth of an inch as compared withany other diameter. After the draw, the diameter could be approximatelyfive-eighths of an inch, and the cross-section -is perfectlycircularwithin acceptable tolerances.

The circular cross-section, drawn rod 20, FIG. 1, is then milled toreduce the circumference at one end to acc'ept a second forming, drawdie. Then, the rod 20, of FIG. 1, is drawn through a second Vaughn drawblock to form a circular cross-section 21 having two longitudinal slotsor grooves 22, 23 extending along the length thereof. If the circularstock of FIG. 1 is initially coiled, the grooves 22, 23 are formed onthe outside of the coil.

Then, the rod 21 is again drawn through a draw block to form a rod 24having grooves 25, 26 of full depth. Under the foregoing assumptionsthat the initial circular cross-section 20 had a diameter offive-eighths of an inch, the completely formed rod 24 has a diameter ofabout .650 inches.

Next, the rod 24 is cut into seven or eight foot lengths andstraightened.

The sacrificial anode rod, per se, cannot easily be used for making aground rod. First, if zinc is used, it is too soft to drive, and second,zinc creeps or cold flows over time and responsive to any added heat.Therefore, if a connector is tightly attached to zinc, the zinc flowsout or creeps away to loosen the point of connection. This looseness, inturn, makes a high resistance electrical joint which generates more heatand causes a still greater cold flow of anode material.

Therefore, to form the sacrificial anode rod 24 into a usable groundrod, a steel reinforcing sheath or jacket 30 (FIG. 4) is given contourscomplementary to the cross-section of the rod. Initially, the steel ispurchased or made to any convenient shape, such as a coiled ribbon.Then, the ribbon is galvanized, preferably with a lock forming quality,hot dipped commercial coat. Next, the ribbon is bent or otherwise formedinto a sheath or jacket having a broken-circular cross-section withhooks or keys 31, 32 turned in at the open ends of the break in thecircle. The hooks 31, 32 provide interlocking edges, add strength andprovide additional material in the area of the rod 24 which is otherwiseweakened by the guideways 25, 26.

The overall inside dimensions of the steel sheath 30 are slightly largerthan the outside dimensions of the anode rod 24. Thus, the rod 24 slipseasily inside the loose steel sheath 30. This looseness is importantsince the softer anode metal does not always yield to the harder steel.Instead, it tends cold flow until it builds-up a lump which is largeenough to bind against the steel and keep the anode rod from slidinginto the sheath.

Next, the loose assembled sheath 30 and anode rod 24 are placed in drawdies 35, 36 and reduced in dimeter in successive steps, as indiated at37, 38 in FIG. 6. If successive passes are made through the dies, thesteel sheath is first reduced to make a perfectly mated sheet-.to-corecombination. Thereafter, and throughout the reduction process, thevolume per cross-section area is the important criteria. As the overallground rod diameter continues to be reduced, the ratio of steel-to-anodecore material antomatically continues to be maintained. Moreover, if azinc core is used and if care is taken to protect the galvanized layerof zinc, all of the exposed metal' is zinc, and all junctions exposed tothe electrolyte are zinc-tozinc junctions; therefore, no galvaniccouples are formed between the steel jacket 30 and zinc core 24.

According to the invention, the completed product forms a drivable,bi-metal sacrificial (with respect to steel) anode ground rod. Briefly,the term drivable implies a metal which is hard enough so that the topWill not mushroom or otherwise deform when it is struck while beingdriven into the ground. The driving tip may encounter a normal number ofstones without becoming unusable, and the rod will not bend anunacceptable amount. The term sacrificial with respect to steel meansthat the anode metal is higher in the galvanic series than steel. By wayof example, one such series is as follows:

Approximate potentials with respect to saturated copper-copper sulphateelectrode, volts* Material:

Commercially pure magnesium l.75.

Magnesium alloy (6 percent Al, 3 percent An, 0.15 percent Mn) 1.6. Zinc1.1. Aluminum alloy (5 percent Zn) l.0. Commercially pure aluminum 0.8.Cadmium 0.8. Mild steel (clean and shiny) -0.5-O.8. Mild steel (rusted)-0.2-0.5. Cast iron (not graphitized) 0.5. Lead -O.5. Tin 0.5. Stainlesssteel, Type 304 (active state) -0.5. Copper, brass, bronze --0.2. Mildsteel (in concrete) -0.2. Titanium -0.2. High silicon cast iron --0.2.Nickel +0.1 to 0.25. Monel 0.15. Silver solder (40 percent) 0.l.Stainless steel, Type 304 (passive state) +0.1. Carbon, graphite, coke5+0.3.

*These values are representative of the potentials normally observed insoils and waters which are neither markedly acid nor markedly alkaline.Of the metals listed in this particular table, magnesium, zinc,aluminum, and cadmium are sacrificial, with respect to steel. Also, itmight be well to point out that a sacrificial anode is a device which isintentionally allowed to disintegrate to protect the steel. Thus, thezinc in a galvanized steel rod is not sacrificial since any sacrifice ofthe zinc would leave the steel without its rust protective coating, andfurther since the total amount of zinc is not adequate to provide asacrificial function.

The ground rod has the strength of steel to withstand the hammer blowswhich drives the rod into the ground and the stones which the rodstrikes as it moves through the ground. More particular, after the zincground rod is reduced to its final diameter a steel drive point 42 isattached to one end and a drive cap 43 is attached to the other end.Again, these parts may be galvanized to preclude the formation of agalvanic couple within the ground rod itself. If it is assumed that thefinished outside diameter of the ground rod is reduced to aboutfiveeighths of an inch in diameter, the anode core 24 is about one-halfinch in diameter. The exposed section 40 of the core is about aquarter-inch at the circumference. This exposed section forms thesacrificial anode.

While the principles of the invention have been described above inconnection with specific apparatus and applications, it is to beunderstood that this description is made only by way of example and notas a limitation on the scope of the invention.

We claim:

1. A sacrificial anode adapted to be driven into the ground andcomprising a sheet steel jacket having generally a C-shaped crosssection enclosing most of the peripheral surface of an elongatedsubstantially straight metal rod of sacrificial metal, the metal of saidrod being higher on the galvanic chart than steel, inturned ends of saidjacket cross section engaging said rod for structurally supporting saidrod along the length thereof and for maintaining surface contact withsaid rod along the length thereof, and said inturned ends definingtherebetween a longitudinal slit in said jacket permitting an elongatedsection of said rod to be exposed as a sacrificial anode through saidslit.

2. An anode as claimed in claim 1, in which the jacket inturned endscomprise a locking key resting within a groove formed in the rod withthe metal of said rod being me.

3. A combined ground rod and sacrificial anode adapted to be driven intothe ground and comprising a steel tubular elongated sheath forming ajacket having an open slot along the full length of said jacket parallelto the length of the sheath, said sheath being crimp connected to anelongated substantially straight inner core of generally uniform crosssection along the length of said core and enclosing most of theperipheral surface of said core said core being fabricated of zinc witha section of the core protruding through the open slot along the lengththereof to form a sacrificial anode.

4. A combined ground rod and anode as claimed in claim 3, in which thecore has at least one groove ex-- tending along the length of the core,and the sheath includes at the edge of the slot at least one looking keyfitting into the groove to lock the core and the sheath together, withsaid jacket compressed against said rod for contact therewith.

References Cited UNITED STATES PATENTS 2,157,180 5/1939 Little 204-1972,829,099 4/1958 Marsh 204-197 3,012,958 12/1961 Vixler 204-1973,391,072 7/1968 Pearson 204-197 TA-HSUNG TUNG, Primary Examiner US. Cl.X.R.

